Indigenous Americans in Canada protesting shale gas and oil exploration on native lands came into conflict with Canadian police in a violent clash that ended with 40 people arrested and several police cars destroyed.

The First Nations, one of the largest indigenous groups in Canada, clashed with police in New Brunswick when protestors tried to block oil and gas exploration by the Houston-based energy company Southwestern Energy Company (NYSE:SWN).

Police used teargas and fired live ammunition in an attempt to disperse the crowd gathered at a Southwestern storage facility. Protestors also blocked key roads used by the company.

Police said firearms and other weapons discovered among the protestors necessitated the use of force to prevent risk to the public, according to Canadian police officials.

The First Nations are protesting the controversial fracking technology being used on their land, a practice that blasts millions of gallons of water and chemicals to shatter deep-rock formations and release petroleum. Environmentalists and other fracking opponents claim the technique contaminates groundwater. The technique has been a major contributor to North America surpassing Saudi Arabia in oil and gas production in the past year.